According to IEEE 802.15.4, this paper presents a total architecture of digital baseband of the Zigbee transceiver. Since the ultra low-power requirement of the Zigbee system, the design greatly simplifies the circuit, and reduces the power consumption. With the simulation of the whole PHY transceiver, which consists of noise modeling in wireless communication channel, the system architecture of the transceiver is determined. The trade-off is made among the parameters, and comparison of the performance with others is given as well.